Maggie Smith and Judi Dench were performing together in a West End play when they received the scripts. They consulted each other, and decided to do the project.
Although they portray sisters who are not twins, Judi Dench and Maggie Smith are almost exactly the same age, being born just nineteen days apart, Dench on December 9, 1934 and Smith on December 28, 1934.
Charles Dance mentioned in his production diary that while they were casting, he got a phone call from Freddie Jones (Jan Pendered), who, having received the script, said "P**s-poor part, but I'll do it because I'm in love with Judi Dench."